18. Real and nominal essence the same in simple ideas and modes, different in substances.
Essences being thus
distinguished into nominal and real, we may further observe, that, in the species of simple ideas and modes, they
are always the same; but in substances always quite different. Thus, a figure including a space between three
lines, is the real as well as nominal essence of a triangle; it being not only the abstract idea to which the general
name is annexed, but the very essentia or being of the thing itself; that foundation from which all its properties
flow, and to which they are all inseparably annexed. But it is far otherwise concerning that parcel of matter which
makes the ring on my finger; wherein these two essences are apparently different. For, it is the real constitution of
its insensible parts, on which depend all those properties of colour, weight, fusibility, fixedness, etc., which are to
be found in it; which constitution we know not, and so, having no particular idea of, having no name that is the
sign of it. But yet it is its colour, weight, fusibility, fixedness, etc., which makes it to be gold, or gives it a right to
that name, which is therefore its nominal essence. Since nothing can be called gold but what has a conformity of
qualities to that abstract complex idea to which that name is annexed. But this distinction of essences, belonging
particularly to substances, we shall, when we come to consider their names, have an occasion to treat of more
fully.
